This application is based on application No.10-251995 filed in Japan on Aug. 22, 1998, the content of which incorporated hereinto by reference.
This invention relates to a chroma key system which replaces background with a separately input image. A chroma key system is shown in FIG. 1. A chroma key system discriminates non-background, such as a human, from the background region of a picture input from a television camera 30. The detected background is replaced by a replacement image separately input from a video tape recorder, a laser disk, or another television camera. Since background is replaced with a different image when a chroma key system is used, it finds use in various applications. For example, a superimposed image of a commentator in front of a country""s weather map is possible, or the commentator""s background can be made into an entirely different scenery.
Prior art chroma key systems discriminate background from non-background by establishing a specific color for the background. In these systems, regions of specified color are taken as background, and regions of color different from the background color are taken as non-background. This discriminates non-background from background. Almost without exception, prior art systems specify blue as the background color, and discriminate blue regions as background and regions that are not blue as non-background.
As described above, prior art chroma key systems which discriminate background from non-background, have the drawback that non-background regions with the same color as the background are mistakenly taken to be in the background. For example, if a non-background commentator wears a necktie with the same color as the background, the necktie will be mistakenly determined to be background. This has the drawback that the region of the commentator""s necktie will be changed into the replacement image. To avoid this problem, prior art requires care that every part of the non-background is not the same color as the background. This has the drawback of putting restrictions on the color of the non-background. In actuality, it is difficult to always make every part of the non-background a different color than the background. This is because the type of subject captured by the camera as non-background is not predetermined.
Therefore, prior art chroma key systems have drawbacks such as mistaken detection of one part of non-background as background and input of another image into that part.
The present invention was developed with the object of solving these types of problems with prior art chroma key systems. Thus a primary object of the present invention is to provide a chroma key system which eliminates non-background color restrictions, and which can accurately discriminate background with the data necessary for image synthesis in the background region screen even, for example, if a map, etc. is displayed or the studio set is used in place of a screen.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The chroma key system of the present invention discriminates background from non-background by color differences. Further, the chroma key system of the present invention does not use a background which always has the same color, but rather is characterized by changing the background color. The changing background color is determined to discriminate background from non-background. The chroma key system of the present invention does not discriminate unchanging color as background. Background is discriminated by changing color under specified conditions. Therefore, the probability of a region of non-background changing color according to the same specified conditions as the changing background color is, in actual practice, approximately equal to zero. Even in the hypothetical case where a non-background region changed color according to the same conditions as the background, background and non-background regions could be correctly discriminated by controlling color changing conditions to be different than that of the non-background.
This type of chroma key system has the characteristic that non-background color restrictions are eliminated and background can be reliably and accurately discriminated. Further, since background and non-background can be discriminated by varying or flashing light in the background region, the system is characterized by allowing information necessary for image synthesis to be displayed on a background screen. In addition, since background can be discriminated when it is varied or flashed according to specified conditions, the background region is not restricted to a screen. Therefore, the system has the characteristic that even the studio set can be used as background. This is because the chroma key system of the present invention does not specify a background color, but rather changes background color and discriminates change in color as background.
The chroma key system of the present invention changes background color by illuminating the background via background illumination equipment. The chroma key system of the present invention uses devices such as light emitting diodes (LED""s), projection television, etc. either alone or in combination as background illumination equipment. Further, in the chroma key system of the present invention, the background may be a television monitor wherein background color is changed by the television monitor. An image display cathode ray tube monitor or an array of many LED""s for full color image display can be used.
The chroma key system of the present invention is provided with background illumination equipment to provide light on the background, a television camera to capture non-background and background, and a background discrimination and swapping circuit to discriminate background from television camera output and replace background regions with a different replacement image. The background discrimination and swapping circuit controls the background illumination equipment to change background color, and discriminates the changing background color to distinguish background regions.
The background discrimination and swapping circuit of the chroma key system of the present invention is configured with a lighting/image control signal generation circuit, a lighting control circuit which changes background color by controlling background illumination equipment via a light control signal output from the lighting/image control signal generation circuit, and a key signal generation and image signal swapping circuit which discriminates background from a discrimination signal output from the lighting/image control signal generation circuit and from the image signal output from the television camera and replaces the background with a replacement image.
In the chroma key system of the present invention, the background illumination equipment may be a projection television. The lighting/image control signal generation circuit outputs a background image signal to the projection television as the light control signal. The key signal generation and image signal swapping circuit discriminates background from the background image signal and from the image signal output from the television camera and replaces the background with a replacement image.